The appearance of outer most (dwarf) planet Pluto has changed significantly in the last two years, after remaining relatively unaltered for the previous 50.
The new images, taken in 2002 and 2003, confirm that Pluto’s surface is actively changing. For reasons that are still mysterious, Pluto’s appearance remained constant for some 50 years of observations before its surface colour became 20 to 30 per cent redder over two years at the beginning of the decade. Over the same period, Pluto’s northern hemisphere also brightened, while its southern hemisphere darkened. This appears to be due to ice vaporising in the sunlit north and refreezing in the wintry south, NASA says.
An explanation may lie in Pluto’s long yet erratic seasons, which can last up to 120 years, with the transformation from winter to summer (such that it is, given temperatures hover at around -200° celsius) causing nitrogen ice to melt and freeze in different hemispheres, thus causing changes in surface colours.